It's exactly the same as catching a regular Pokemon. Try to weaken it enough for its HP bar to turn red. The move False Swipe can get its HP down to 1. Also try giving it a status effect like paralyzing it or putting it to sleep. Also, use high-level balls like Ultra Balls to get an even better chance.
If all else fails, you can just use a Master Ball if you have one.
Yes, Pokemon Sapphire version is the version in which you can catch Latias. You can only find it once you have beaten the Pokemon League, then there is a report of a legendary red flying Pokemon in Hoenn. Latias appears randomly.
Yes. Kyogre is the main legendary Pokemon in Sapphire.
Hatch? No. No legendary Pokemon can be bred in any Pokemon version. You can catch Kyogre in Sapphire though ;)
You catch them with a ultra ball
In order to catch your legendary Pokemon in Pokemon Sapphire, save your master ball For Rayquaza...you can catch KYogre/Groudon/both with either an Ultra Ball or Timer Ball.
Catch it in route 116
you can't catch it in any version
Kyogre only.
you must die
Best non-legendary water pokemon would be Gyarados. Best legendary water pokemon is Kyogre.
5
Sadly, you can't catch Groundon is the Sapphire Version, however you can in the Ruby version, you will find him in the same place you find Kyorge in the sapphire version.